A little cleanup.
Improve watch handling of integers.
Split slider classes again.

The previous failed commit, which created one base class for sliders,
did not account for the treatment of the double and integer types as
they were loaded from files, causing files using integer sliders with
the previous build to fail to load their saved values. This commit
removes the shared slider base class in favor of an ISlider interface,
and adds additional checks to ensure that slider mins, maxes, and steps,
automatically reset to appropriate values during changes, and handle
culture invariant formatting correctly.
Rename SliderBase file to ISlider.
Update the NodeViewCustomizations for sliders.
Fix TestDoubleInput test.
Merge remote-tracking branch 'origin/master' into SliderFixes
Merge pull request #3454 from DynamoDS/SliderFixes

Fixes for regressions introduced by #3404